Mech stability through gyroscope

Question

I recently read up about gyroscopes, angular momentum and mechs (the big Cockpit controlled robots) and was wondering if it would be possible to get a stable walking mech (only as example, not meant to be a serious attempt http://autopixx.de/bilder/lM23mgzq/battle-mech.jpg) by adding a big enough gyroscope which stabilizes the mech as it lifts a leg in the walk cycle. The mech is about 4 meters high, but I can't speculate on how much it probably would weight.

Just a question out of curiosity. Thanks in advance :)

Answer 1

Gyroscopes precess. That means if you apply force to change the direction of their axis of rotation, the axis actually moves at right angles to that force. The faster they are spinning, the more force it takes.

A simple example is the front wheel of a bicycle or motorcycle. If you are traveling at speed, and you press forward on the right handlebar (as if you wanted to turn the wheel to the left) what happens is the wheel doesn't turn in the direction you are pushing it; instead it precesses and tilts you to the right. So to initiate a right-hand turn, act as if you want to turn left!

As another example, the WW1 aircraft, the Sopwith Camel, had a rotary engine. In other words, the entire cylinder block rotated, making a powerful gyroscope. So pitch inputs would result in strong yaw precession, and vice-versa, killing inexperienced pilots.

So if you want to stabilize a walking platform with a gyroscope, keep in mind that it doesn't always point in the same direction. You have to provide right-angle corrective forces to make it point in the direction you want.

ADDED: You might be wondering why car wheels don't do the same thing. The answer is that they want to but can't. So if you press the steering wheel to the left, the wheels want to precess so they would be tilted to the right. Since they are constrained so they can't tilt to the right, this generates a force trying to tilt them upright. That force causes the wheel to precess in the direction you originally tried to turn it! So it acts as if you can easily turn it to the left, but there are precession forces being born by the wheel bearings.

NOT TO BELABOR, but there's a very simple way to understand precession. Don't think of the gyroscope as a solid wheel. Think of it as a bunch of independent weights connected to the hub by strings. So imagine taking your bicycle and elevating it off the ground, and spinning the front wheel (in the normal direction), thinking of it as a bunch of independent weights spinning. Applying a force to try to turn it to the left is like placing your hand against the stream of weights at the front of the wheel (where they are descending) and trying to push them to the left. Rather than moving to the left, they bounce off your hand into a slanted direction down and to the left. So then they are orbitting in a slanted direction. That's precession.

Answer 2

Short answer: I believe, yes, it is possible.

But what you likely will want is a Control Moment Gyroscope (CMG) - multiple "gimbaled" gyros operating in tandem, with their orientation controlled by small actuators and a computer. With this approach you can not only help keep things balanced but shift large amounts of torque around with minimal effort - making something lean, turn on any axis, etc. The space station uses a set of four CMG to change its attitude already.

Naturally the gyros will have to be heavy and/or spin very quickly to make the momentum you are after. (Explosion mitigation will be necessary with such an arrangement as it spins so fast and material of flywheel can rip apart.)

For a real-world example, there is a near-production self balancing motorcycle (Lit Motors C-1) that uses this exact approach to keep an 800lb vehicle balanced even while being dragged by a truck or body-slammed by some men. It is said to provide 1,300 lb-ft of torque, using 2x42lb gyros in their CMG spinning at 8-12K RPM. And they believe they provide even more. Have a look at their patent.

I suggest you compute the weight you want to control. Then use that as a basis for calculating what kind of force you need to counter to keep your mech from tipping over.